Research On The Preparation And Interconnect Performance Of Cu@Ag@In Core-shell Structure Powder

The power density has increased significantly as the power semiconductor modules become miniaturized and integrated.It dissipates a large amount of heat when devices working,and poses a challenge to the high-temperature resistance of the solder joint.As the passageway between components and substrate,solder joints need to have excellent electrical,thermal,and mechanical properties.At the same time,it is also able to work under a certain high temperature to confirm the development of a high-power device.A new type of interconnect material based on Cu@Ag@In core-shell structure is proposed,which is characterized by the rapid consumption of a low melting point phase inside the Ag-In system.The core of the material is Cu,Ag layer severs as the intermediate reaction and In-shell for low-temperature bonding,which formed a three-layer core-shell structure.And the Ag In₂/In layer outside the shell can be quickly consumed to form a high-temperature resistance solder joint.The Cu@Ag@In metal powder was prepared by electroless plating method,and the orthogonal experiment method was applied to the process research of coating thickness control.It was found that the concentration of glucose and silver salt temperature had a significant effect on the thickness of the silver coating layer,temperature as well.The concentration of Indium sulfate and sodium borohydride had a general effect on the Indium coating（Indium-containing layer）.Cu@Ag@In metal powder that could be used for connection is prepared through multiple plating by increasing the thickness of Ag In₂/In layer.The structure and properties of solder joints were analyzed,whose interconnections formed by powder preform.The internal structure of Cu@Ag@In core-shell metal powder was Cu,Ag,Ag-In intermetallic compound and In from the inside to the outside.Cu@Ag@In powder-preformed-tablet could be formed into a perfect shape.It also could be cut into a specific size for interconnection according to pads.And it had excellent electrical and thermal conductivity after reflow,which had a resistivity of 11.3μΩ·cm and thermal conductivity of 68.32 W·m^-1·K^-1.After that,the interconnection process was explored and joints could be formed effectively in the condition of low-temperature and short-time.The average shear strength of solder joints could reach 19.6 MPa at room temperature and 18.6 MPa at 250℃.It would be higher if increasing temperature and pressure,as well as extending the holding time.In elements diffuse into the Cu core with the joint enlistment for a long time,at a high-temperature of 300℃.The shear strength of the solder joints was in accordance with the packaging requirements of power devices for mounting materials during the aging process.The shear strength of the joint enhanced during the process that Cu-In intermetallic compound layer was formed at the core-shell interface,and the"grid-like"Ag₉In₄ transforms into a silver-rich solid solution.The pores in the Ag-In compound layer increased,which was believed to be caused by the volume change during the phase transition and Kirkendall voids.While it would come into being cracks because of the internal defects of the preform,which reduces the reliability of the joints.